Microstructures produced on spatially confined substrates exposed to repetitively pulsed laser radiation

The formation of microstructures is studied on metal substrates with characteristic dimensions of tens of micrometers that are comparable with the period of structures produced on extended substrates. Experiments were performed with nickel and nichrome targets composed of wires or a foil. Targets were irradiated in air by 510-nm, 20-ns pulses from a copper vapour laser operating at a pulse repetition rate of 7.5 kHz. Irradiation produced microcones and circular microstructures on substrates. The influence of the target geometry on the morphology and ordering of microstructures formed on it is demonstrated experimentally. The specific features of structures produced on spatially restricted targets are explained by the influence of boundary conditions on their development. A mathematical model of the initial phase of formation of the inhomogeneous profile of the surface of spatially restricted substrates exposed to laser radiation is proposed.